Embedded Operating Systems and Linux Amir Hossein Payberah payberah@gmail.com 1
Agenda ➲ Embedded Systems ➲ Real Time Systems ➲ Who Are The Players? ➲ Linux As An Embedded OS ➲ Kernel 2.4 vs. 2.6 ➲ Applications And Products ➲ The Embedded OS Market 2
Embedded Systems 3
What is an Embedded OS? ➲ An "embedded system" is any computer sys- tem or computing device that performs a ded- icated function or is designed for use with a specific embedded software application. ➲ Embedded systems may use a ROM-based op- erating system or they may use a disk-based system, like a PC. But an embedded system is not usable as a general purpose computers or devices. 4
What makes a good Embedded OS? ➲ Modular ➲ Scalable ➲ Configurable ➲ Small footprint ➲ Device drivers ➲ etc, etc, etc... 5
Real Time Systems 6
What is Real Time? “A real time system is one in which the correct- ness of the computations not only depends upon the logical correctness of the computation but also upon the time at which the result is produced. If the timing constraints of the sys- tem are not met, system failure is said to have occurred.” Donald Gillies 7
What is Real Time? “Real time in operating systems: The ability of the operating system to provide a required level of service in a bounded re- sponse time.” POSIX Standard 1003.1 8
Hard vs. Soft Real Time ➲ Hard ● Absolute deadlines that must be met ● Example: Braking system controller ➲ Soft ● Time tolerance within which an event can occur ● Example: Multimedia streaming 9
What makes a good Real Time OS? ➲ Multi-threaded and pre-emptible ➲ Thread priority has to exist ➲ Must support predictable thread synchron- ization mechanisms ➲ A system of priority inheritance must exist 10
Who are the players 11
Who are the Embedded OS players? ➲ Wind River Systems ● VxWorks ● pSOS ➲ QNX Software Systems ● QNX ➲ Green Hills Software ● Integrity 12
Who are the Embedded OS players? ➲ Mentor Graphics ● VRTX ➲ Palm Computing ● PalmOS ➲ Symbian ● SymbianOS 13
Who are the Embedded OS players? ➲ Windows ● Embedded NT/XP “Real-time” control ● ● Windows CE (CE.NET) Internet devices ● ● Pocket PC 2002 Handheld PC’s and PDA’s ● 14
Linux as an Embedded and Real Time system 15
GNU History ➲ In 1983 ➲ Richard Stallman ➲ It is free ● free means freedom ➲ GNU's Not Unix 16
Linux History ➲ In 1991 ➲ Linus Torvalds ➲ Based on Minix ➲ GNU/Linux 17
What’s so special about Linux? ➲ Multiple choices vs. sole source ➲ Source code freely available ➲ Robust and reliable ➲ Modular, configurable, scalable ➲ Superb support for networking and Internet ➲ No runtime licenses ➲ Large pool of skilled developers 18
What’s so special about Linux? 19
What’s special about Open Source? 20
Commercial Embedded Linux ➲ AMIRIX Embedded Linux Derived from Debian ● ➲ Coollogic Coollinux Combines Linux and Java for Internet apps ● ➲ Coventive Xlinux Kernel can be as small as 143KB ● ➲ Esfia RedBlue Linux 400K, designed for wireless apps ● 21
Commercial Embedded Linux ➲ KYZO Pizza Box Linux SAMBA based file, print, CD server ● ➲ Lineo Embedix Supports real time and high availability apps ● ➲ LynuxWorks BlueCat General purpose embedded solution ● ➲ MontaVista Linux General purpose embedded solution ● 22
Commercial Embedded Linux ➲ Neoware NeoLinux Red Hat derived for information appliances ● ➲ PalmPalm Tynux Internet appliance and multimedia ● ➲ Red Hat Embedded Linux General purpose embedded solution ● ➲ RedSonic Red-Ice Linux Runs from DiskonChip or CompactFlash ● 23
Commercial Embedded Linux ➲ RidgeRun DSP Linux For multimedia, wireless, RT on DSP ● ➲ TimeSys Linux GPL Low latency enhanced kernel ● ➲ Tuxia TASTE Distro targets Internet appliances ● ➲ Vital Systems vLinux For ARM based embedded apps ● 24
Open Source Embedded Linux ➲ Embedded Debian Project Convert Debian to an embedded OS ● ➲ ETLinux It is small, modular, flexible and complete ● ➲ uCLinux For microprocessors that don’t have MM ● ➲ uLinux (muLinux) Distro fits on a single floppy ● 25
Commercial Real Time Linux ➲ FSMLabs ● Open RT Linux ➲ Lineo ● Embedix Realtime ➲ LynuxWorks ● BlueCat RT 26
Commercial Real Time Linux ➲ MontaVista Software ● Real Time Extensions ➲ REDSonic ● REDICE Linux ➲ TimeSys ● Linux/Real-Time 27
Open Source Real Time Linux ➲ RT Linux “Hard” Real Time Application Interface ● ➲ RTAI “Hard” Real Time Application Interface ● ➲ KURT Event schedules with 10us resolution ● ➲ Linux-SRT For soft real time apps like multimedia ● ➲ Qlinux Provides Quality of Service guarantees ● 28
Commercial or Open Source Linux 29
What makes them different? ➲ Which of Linux utilities are included ➲ What modules or utilities added ➲ What kernel patches and modifications are provided ➲ How the installation, configuration, main- tenance, and upgrade process is managed. 30
How to create Embedded Linux? ➲ Leaving out modules you don't need ➲ Changing configuration 31
How to create Embedded Linux? ➲ Linux is not a real-time operating system The kernel disables interrupts ● The kernel is not suitably preemptible ● ➲ Using the dual-kernel system A general purpose (non-real-time) OS runs as a ● task under a real-time kernel. The general purpose OS provides functions such ● as disk read/write, LAN/communications, serial/parallel I/O, system initialization, memory management, etc. The real-time kernel handles real-world event ● processing. ➲ Modifying the Linux kernel 32
Linux kernel architecture 33
Providing Real Time Service within Linux ➲ Preemption improvement ➲ Interrupt abstraction 34
Preemption improvement ➲ Modifying the Linux kernel code to reduce the amount of time that the kernel spends in non-preemptible sections of code. ➲ It is used to implement soft real time sys- tems. 35
Preemption improvement 36
Interrupt abstraction ➲ The entire kernel is made preemptible by hav- ing a separate hardware-handling layer. ➲ This hardware abstraction layer has complete control over the hardware interrupts, and simulates the inter- rupts up to the Linux kernel in a way that allows the ker- nel to run unmodified on the real-time scheduler. ➲ This system is often described as a micro-kernel system. where the full Linux kernel runs as the lowest priority ● task alongside real-time tasks in the system on top of the real-time scheduler. ➲ It is used to implement hard real time systems. 37
Interrupt abstraction 38
RTLinux and RTAI ➲ Interrupt abstraction ➲ Hard real time ➲ Real time tasks are operating in kernel space ➲ Real-time tasks are written to the API of RTLinux or RTAI, not to the Linux API. ➲ RTAI offers an alternative to kernel-space operation, in the form of LXRT. LXRT supports the same API as RTAI, but via tasks that run ● in user-space. ➲ The recent announcement of RTLinux V3.0 pre-7 also in- troduces user-space real-time in RTLinux. In this model, a function in user address space may be ac- ● tivated by an interrupt or timer. 39
MontaVista and TimeSys ➲ Preemption improvement ➲ Hard real time ➲ They use preemtible kernel This preemption cannot be done safely at arbitrary ● places in the kernel code (critical sections). ➲ They alter the spin-lock calls to additionally prevent preemption. ➲ They use separate real time kernels. Interrupt abstraction ● MontaVista uses RTLinux ● TimeSys uses RTAI ● 40
Kernel 2.4 vs. 2.6 41
Linux Kernel 2.4 vs. 2.6 42
Device Drivers and Loadable Kernel Modules The Linux 2.6 kernel introduces a new, unified framework for ➲ device drivers. The new driver model provides a framework for full and com- ➲ plete support for device Plug and Play and power manage- ment by defining the interfaces that these subsystems can use when communicating with individual drivers. The new driver framework provides a much cleaner separation ➲ of responsibilities between buses and drivers. The 2.6 Linux kernel also introduces the sysfs filesystem to ➲ provide a hierarchical view of each system's device tree. The 2.6 Linux kernel also introduces a new naming convention ➲ for loadable kernel modules, using the .ko extension (kernel object) rather than the standard .o (object) extension used for loadable kernel modules in all previous stable releases of the Linux kernel. 43
Verifying and updating critical packages 44
Real Time Linux Alternatives 45
Applications and Products 46
What’s It Being Used For? ➲ Control and Monitoring Applications ➲ Industrial Controllers ➲ TV Set Top Boxes (TiVO) ➲ Handheld PDA’s ➲ Automobile Computers ➲ Telecomm and Networking Hardware ➲ Other uses... 47
Cyclades TS-100 (Console Server) ➲ Netlinos OS ➲ Dual 50MHz PowerPC ➲ 16MB SDRAM 4MB Flash ➲ Ethernet/Serial/RS485 48
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